The invention relates to a vertical cavity surface emitting laser, VCSEL.
A VCSEL is an injection diode laser where the laser oscillation and output occur normal to the pn junction plane, "Surface Emitting Semiconductor Lasers", Kenichi Iga et al, IEEE Journal of Quantum Electronics, Vol. 24, No. 9, September 1988, pp. 1845-1854 and "GaAs Vertical-Cavity Surface Emitting Lasers Fabricated by Reactive Ion Etching", Kent D. Choquette et al, IEEE Photonics Technology Letters, Vol. 3, No. 10, October 1991, pp. 859-862. Desirable properties include low divergence circular output, single longitudinal mode operation, and high two-dimensional packing density for arrays, which makes VCSELs attractive for applications such as optical recording, communications, and computing.
Most applications of semiconductor lasers require dynamic stabilization and control of the light output, which in turn requires a feedback circuit from a detector to the forward biasing circuit controlling laser injection. It is known to provide a separate light detector for monitoring the laser light output, and providing a feedback connection from the detector to the circuit forward biasing the VCSEL diode. It is also known to monolithically integrate a photodiode on either the top or the bottom of the VCSEL such that the axially vertically emitted light impinges the photodiode, and the latter provides the feedback signal, "Monolithic Integration of Photodetector With Vertical Cavity Surface Emitting Laser", G. Hasnain et al, Electronics Letters, Vol. 27, No. 18, Aug. 29, 1991, pp. 1630-1632. While the monolithic integration of the laser and detector should result in lower packaging cost, it has been found that the structure is too complex and costly to manufacture.
The present invention provides an integrated VCSEL and detector combination which is particularly simple and cost effective. Lateral horizontally emitted light from the VCSEL diode is monitored as an indication of the axially vertically emitted light. One or more of the VCSEL diodes on the substrate is used as a detector. The remaining VCSEL diodes are forward biased in normal manner for laser injection, and emit light vertically axially and horizontally laterally. The lateral light impinges the detector diode to cause current flow therein, which current is monitored, to provide a feedback signal for controlling the forward biasing circuit for the lasing diodes. The invention enables the noted detection for feedback control in a monolithic integrated structure, without a separate detector, and without special or additional crystal growth and processing steps otherwise required for a vertically integrated detector. The invention enables the existing structure of a VCSEL to be used.
The invention also provides an electrical-optical-electrical transducer wherein electric current in the forward biasing circuit for the lasing diodes stimulates laser light emitted horizontally laterally which in turn impinges a laterally adjacent non-lasing VCSEL diode to cause current flow therein.